Let us consider the first order nonlinear wave equation describing
the propagation in the positive direction of the x-axis of a wave
where propagation speed 
is a given
function of 
:
This nonlinear equation, studied in [6], is known to
``propagate'' in space an initial profile 
with velocity
:
Figure 1: Successive profiles at position x=0, x=L
The propagation time throught a
waveguide from input to output 
depends on the magnitude of the
input wave and on the length L of the guide:
